In 711 Iberia was invaded by a Muslim army commanded by Tariq ibn Ziyad. The last Visigothic king, Rodrigo, tried to repel this invasion but was defeated. The Muslims advanced to Córdoba and then to Toledo, the Visigothic capital. The last resistance of the Visigoths was made at Mérida, which fell in June 713 after a long siege. In the spring of 714, a Muslim army commanded by Musa ibn Nusair marched to Saragossa and then to León and Astorga. Évora, Santarém, and Coimbra fell by 716. Thus, within five years, the Muslims had conquered and occupied the entire peninsula. Only a wedge of wet, mountainous territory in the extreme northwest called Astúrias remained under Christian control.

In Lusitania land was divided among Muslim troops. However, bad crops and a dislike for the wet climate put an end to the short-lived Muslim colonization along the Douro River. Muslims preferred the dry country below the Tagus River because it was more familiar, especially the Algarve, an area of present-day Portugal where the Muslim imprint remains the strongest. The Muslim aristocracy settled in towns and revived urban life; others fanned out across the countryside as small farmers. The Visigothic peasants readily converted to Islam, having only been superficially Christianized. Some Visigothic nobles continued to practice Christianity, but most converted to Islam and were confirmed by the Muslims as local governors. Jews, who were always an important element in the urban population, continued to exercise a significant role in commerce and scholarship.

Al Andalus, as Islamic Iberia was known, flourished for 250 years, under the Caliphate of Córdoba. Nothing in Europe approached Córdoba's wealth, power, culture, or the brilliance of its court. The caliphs founded schools and libraries; they cultivated the sciences, especially mathematics; they introduced arabesque decoration into local architecture; they explored mines; they developed commerce and industry; and they built irrigation systems, which transformed many arid areas into orchards and gardens. Finally, the Muslim domination introduced more than 600 Arabic words into the Portuguese language.

The Golden Age of Muslim domination ended in the eleventh century when local nobles, who had become rich and powerful, began to carve up the caliphate into independent regional city-states (taifas), the most important being the emirates of Badajoz, Mérida, Lisbon, and Évora. These internecine struggles provided an opportunity for small groups of Visigothic Christians, who had taken refuge in the mountainous northwest of the peninsula, to go on the offensive against the Muslims, thus beginning the Christian reconquest of Iberia.

Data as of January 1993